How do I fade music in and out using Blender?
I trust your  using the video sequence editor in Blender? Load your video strip and sound/music strip into separate channels. Select the music strip press the N key to access the properties panel on the right hand side of the screen. Under the Sound tag you'll see a Volume slider. If you wish to fade the music in at the start, go to frame 0 and set the volume to 0 in the slider. Hover your mouse over the slider and press the I key to set a keyframe. The slider background should change colour, colour depends on your Blender Theme.

Now go to the point on the time line say frame 60 and set the volume to 1 or what ever level you would like at this point and hover the mouse over the volume slider and press the I key to set another keyframe. The music will fade in from 0 - 1 over these frames.

Fading out is the reverse process, go to where you want the fade to start; make sure the volume is level 1 hover over the slider and press I to set a keyframe. then go to the end of the clip set the volume to '0' and set another keyframe.

Note if you don't set the key frame to 1 near the end of the clip the volume will fade from the first keyframe set to 1 at the beginning down to 0 for the keyframe at a the end.






Hope this helps.